Infinite SEO Generated Sitemap Error Line 2

I was just curious about how my website's sitemap generated by Infinite SEO is and I went to mydomain.com/sitemap.xml and I received the error at the top of my page (look at screenshot to see error).

Infinite SEO hasn't been telling me about this and not so sure what the problem is. I've been using the plugin for over a month... this doesn't seem good though, so reporting it here.

Would a staff member help me diagnose and resolve this issue? Please respond ASAP. Thanks in advance!